Driver circuit having preslewing circuitry for improved slew rate control

A driver circuit having a slew rate control system, comprising:

• a first source of current having a first terminal and a second terminal, with the first terminal coupled to a first reference voltage;
• a second source of current having a first terminal and a second terminal, with the second terminal coupled to a second reference voltage, wherein the first source of current is of larger magnitude than the second source of current;
• a first switch, having a first terminal and a second terminal and being provided with a control signal, with the first terminal of the first switch coupled to the second terminal of the first source of current and with the second terminal of the first switch coupled to the first terminal of the second source of current;
• a second switch, having a first terminal, a second terminal, a third terminal, and the control signal as an input signal, with the first terminal of the second switch coupled to the first terminal of the second source of current and the second terminal of the second switch coupled to a third reference voltage characterized as having a lower magnitude of voltage than the first reference voltage;
• a first conductive device having a controllable conduction path, with a first terminal of the first conductive device coupled to the first terminal of the second source of current and the first terminal of the second switch, a second terminal coupled to a conductive device reference voltage, and a control terminal coupled to the third terminal of the second switch;
• a capacitive element having a first terminal coupled to the first terminal of the second source of current, the first terminal of the first switch, the first terminal of the first conductive device, and the first terminal of the second switch and having a second terminal coupled to a capacitive element reference voltage;
• an amplifier having a first input terminal, a second input terminal and an output terminal, with the first input terminal coupled to a node at the first input terminal formed by the coupling of the first terminal of the capacitive element, the first terminal of the conducting element, the first terminal of the second switch, the first terminal of the second source of current, and the first terminal of the first switch, wherein the second input terminal is an inverting input terminal, the first reference voltage is applied to the amplifier, and the amplifier generates a voltage on the output terminal;
• a power device, having a control terminal, a first terminal, a second terminal and characterized as having a conduction path between the first terminal and the second terminal, wherein the control terminal receives the voltage generated by the amplifier and controls conduction of the power device, the first terminal is coupled to the third reference voltage, the second terminal is coupled to the second input terminal of the amplifier, and an output voltage of the power device is resident on the second terminal of said power device,
• wherein the first conductive device conducts only when the control signal is the first logic level and the voltage generated by the amplifier is larger than the third reference voltage and the first conductive device will conduct until the voltage at the node at the first input terminal of the amplifier is reduced to be approximately equal to the third reference voltage,
• wherein when the control signal transitions from the first logic level to the second logic level the first switch conducts, the first source of current delivers a charging current to the capacitive element as the second source of current delivers a discharging current to the capacitive element resulting in a net charging current being supplied to the capacitive element, the output voltage generated by the power device increases to the third reference voltage, and a voltage on the control terminal of the power device increases to the first reference voltage, and
• wherein when the control signal transitions from the second logic level to the first logic level, the first switch does not conduct, the first source of current will not charge the capacitive element, the first conductive device conducts so long as the output voltage generated by the power device is larger than the third reference voltage, and the second source of current operates to quickly discharge the capacitive element so that the voltage at the node at the first input terminal of the amplifier is quickly reduced until the voltage at the node is approximately equal to the third reference voltage.